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The above output is trimmed, but each folder will contain a plist file for each respective user, computer, or group in the local directory. Accounts that begin with an underscore (_) are hidden service users and groups. For example, the web server uses the_www account, which obtains user settings from the _www.plist file. The _www user can t log in because the account has no shell or password. If you created a new user in the above section, look in the /private/var/db/dslocal/nodes/Default/users directory and you should see a .plist file with a name that corresponds to the new user s short name.

Inside a .plist file there are a number of attributes containing data about a given user or group. Looking at local users and groups from a Microsoft Windows perspective, files in the local directory node resemble registry keys for local accounts. Examine the .plist file for the user created earlier and look for the key called authentication_authority.

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This key specifies the service that will be utilized to authenticate the user. Notice that it says ShadowHash, which indicates that the system will use a local file called a hash file to authenticate the user. Mac OS X password hash files contain copies of a user s password in multiple formats; this Rosetta Stone allows for different services to authenticate a user with their own native password encryption type. If this were not the case, the password would need to be stored in a much less secure reversible hash in order to support the various authentication schemes out there. It also should be noted that for ShadowHash users, any network service that does not support SHA-1 (Secure Hash Algorithm 1) or NTLM (NT LAN Manager) authentication will require cleartext authentication; SSL is highly recommended in these scenarios. In the user s plist file, you will also see a generateduid key, which is used to track the user account even if the short name is changed. GeneratedUIDs are based on a standard called the Universally Unique IDentifier (UUID), which is a complex, programmatically generated string of characters that will never be duplicated in our lifetime. A UUID is unique across time and space for every user. If you look in the /private/var/db/shadow/hash directory, you will find a file that is named using the value of this key. This means that even if a user account s username is changed, the password will still be tied to that account. Moreover, it prevents stale password files from collecting, which would happen if passwords were based on the short name. In 10.4 and later, the password hash file will contain at least a SHA-1 salted hash for the user, which is a secure, unrecoverable password type. If Windows file-sharing services are enabled for the user, it will also contain the respective NTLM hash for that user, which is used by our Windows file-sharing components. Apple has struggled to implement the best balance of security and functionality in regard to password hashes. While hashes for Windows file sharing require NTLM, the NTLM hash type is more susceptible to common password attacks, which makes its recoverability more feasible. Apple only enables the NTLM hash when Windows file-sharing users are specifically configured for SMB/Windows sharing access in the System Preferences Sharing pane. Storing passwords in a hash file allows for a consistent password file location, with flexible extensibility for other password hashes such as NTLM. In the above example, the authentication_authority record, which has a value of ;ShadowHash;, tells the local directory service to consult the user s local hash file when the user attempts to authenticate. The data from the account property lists can be managed by modifying the text files directly. For example, if you want to change a user s picture, you could alter the picture key. However, editing property lists directly can be pretty cumbersome, so Apple has